1. Field of the Invention
This invention relates to a pattern finding apparatus. This invention particularly relates to a pattern finding apparatus wherein, from an image signal made up of a series of image signal components representing a radiation image of an object, a judgment is made as to whether a predetermined picture element P0 in the radiation image falls or does not fall within the region corresponding to a predetermined pattern, such as a blood vessel pattern, in the radiation image. This invention also relates to a linear pattern width calculating apparatus, wherein a calculation is made to find the width (or the thickness) of a linear pattern, such as a blood vessel pattern or a rib pattern, which may appear in a radiation image. This invention further relates to an abnormal pattern detecting apparatus, wherein an abnormal pattern appearing as an approximately circular pattern in a radiation image of an object is detected from an image signal made up of a series of image signal components representing the radiation image.
2. Description of the Prior Art
Techniques for reading out a recorded radiation image in order to obtain an image signal, carrying out appropriate image processing on the image signal, and then reproducing a visible image by use of the processed image signal have heretofore been known in various fields. For example, as disclosed in Japanese Patent Publication No. 61(1986)-5193, an X-ray image is recorded on an X-ray film having a small gamma value chosen according to the type of image processing to be carried out, the X-ray image is read out from the X-ray film and converted into an electric signal (image signal), and the image signal is processed and then used for reproducing the X-ray image as a visible image on a copy photograph, or the like. In this manner, a visible image having good image quality with high contrast, high sharpness, high graininess, or the like, can be reproduced.
Also, when certain kinds of phosphors are exposed to radiation such as X-rays, .alpha.-rays, .beta.-rays, .gamma.-rays, cathode rays or ultraviolet rays, they store part of the energy of the radiation. Then, when the phosphor which has been exposed to the radiation is exposed to stimulating rays such as visible light, light is emitted by the phosphor in proportion to the amount of energy stored thereon during its exposure to the radiation. A phosphor exhibiting such properties is referred to as a stimulable phosphor. As disclosed in U.S. Pat. Nos. 4,258,264, 4,276,473, 4,315,318, 4,387,428, and Japanese Unexamined Patent Publication No. 56(1981)-11395, it has been proposed to use stimulable phosphors in radiation image recording and reproducing systems. Specifically, a sheet provided with a layer of the stimulable phosphor (hereinafter referred to as a stimulable phosphor sheet) is first exposed to radiation, which has passed through an object, such as the human body. In this manner, a radiation image of the object is stored on the stimulable phosphor sheet. The stimulable phosphor sheet, on which the radiation image has been stored, is then scanned with stimulating rays, such as a laser beam, which cause it to emit light in proportion to the amount of energy stored thereon during its exposure to the radiation. The light emitted by the stimulable phosphor sheet, upon stimulation thereof, is photoelectrically detected and converted into an electric image signal. The image signal is then used during the reproduction of the radiation image of the object as a visible image on a recording material, such as photographic film, on a display device, such as a cathode ray tube (CRT), or the like.
Radiation image recording and reproducing systems which use stimulable phosphor sheets are advantageous over conventional radiography using silver halide photographic materials, in that images can be recorded even when the energy intensity of the radiation to which the stimulable phosphor sheet is exposed varies over a wide range. More specifically, since the amount of light which the stimulable phosphor sheet emits when being stimulated varies over a wide range and is proportional to the amount of energy stored thereon during its exposure to the radiation, it is possible to obtain an image having a desirable density regardless of the energy intensity of the radiation to which the stimulable phosphor sheet was exposed. In order to obtain the desired image density, an appropriate read-out gain is set when the emitted light is being detected and converted into an electric signal to be used in the reproduction of a visible image on a recording material, such as photographic film, or on a display device, such as a CRT.
Recently, in the radiation image recording and reproducing systems which use X-ray film or stimulable phosphor sheets, particularly in such radiation image recording and reproducing systems designed to facilitate medical diagnoses, not only have image signals been processed in ways which ensure that the visible images produced from them will be of high quality, but image signals have also been processed in ways which allow certain image patterns to be extracted from radiation images. One type of processing which results in extraction of an image pattern is disclosed in, for example, U.S. Pat. No. 4,769,850.
Specifically, an image pattern can be detected in a complicated radiation image by processing the image signal representing it in various ways. The image signal is made up of a series of image signal components, and with appropriate processing the image signal components corresponding to a particular image pattern can be found. For example, from a very complicated radiation image, such as an X-ray image of the chest of a human body, which includes various linear and circular patterns, an approximately circular pattern corresponding to a tumor, or the like, can be detected.
After a pattern, for example, a tumor pattern, is detected in a complicated radiation image, such as an X-ray image of the chest or a mammagram of a human body, a visible image is reproduced and displayed such that the detected pattern can be viewed clearly. Such a visible image can serve as an effective tool in, particularly, the efficient and accurate diagnosis of an illness.
When an image pattern is to be detected, operations are often carried out to find a linear pattern in a radiation image, for example, a pattern of a blood vessel in an X-ray image of a human body. The operations for finding a blood vessel pattern are carried out when a reproduced visible image, in which the blood vessel pattern is illustrated clearly, is to be obtained. Alternatively, the operations for finding a blood vessel pattern are carried out when the blood vessel pattern need not be illustrated clearly in a reproduced visible image but, for example, a tumor pattern (an approximately circular pattern) is to be detected from an X-ray image of a human body. Specifically, an X-ray image of a human body has a very complicated configuration. For example, an X-ray image of a human body includes a pattern of a branch point of a blood vessel, at which the blood vessel divides into two branches, and a pattern of a blood vessel, which extends in the direction normal to the plane of the X-ray image, i.e. in the direction along which the X-rays were irradiated during the recording of the X-ray image. Such blood vessel patterns are approximately circular. Therefore, when a tumor pattern is to be detected, such approximately circular blood vessel patterns are often detected as tumor patterns. Accordingly, accurate operations for finding a tumor pattern should be carried out by discriminating whether a pattern, which has been detected as a tumor pattern, is a true tumor pattern or an approximately circular blood vessel pattern. For this purpose, it is necessary for a blood vessel pattern to be found.
As described above, it often becomes necessary that a linear pattern in a radiation image be found. In such cases, a method should be selected with which a linear pattern can be found accurately.
An example of a filter for finding a linear pattern is disclosed in U.S. Pat. No. 4,769,850. However, with the disclosed filter, the results of the filtering process are obtained which depend on the image density of the areas surrounding a linear pattern. Specifically, the problem occurs in that the sensitivity, with which a linear pattern is found, varies for a linear pattern located in a high image density region of a radiation image and a linear pattern located in a low image density region of a radiation image.
Another example of a filter for finding a linear pattern is described in "Discrimination of Blood Vessel Patterns in X-ray Fluorographic Image of the Chest" by Jun-ichi Hasegawa, et al., Medical Electronics And Somatology, pp. 36-42, September 1984. However, this linear pattern finding filter has directional properties. Specifically, with this linear pattern finding filter, only a linear pattern extending along a specific direction is discriminated. Therefore, this linear pattern finding filter is not suitable for the discrimination of linear patterns, such as blood vessel patterns, which extend in various different directions.